fix empty list errs

app.py

@@ -38,7 +38,7 @@ def generate_response(outputs, new_prompt):
 
 def undo(outputs):
 
-    outputs = outputs[:-1] if outputs else None
+    outputs = outputs[:-1] if outputs else []
     return {
         user_outputs: outputs,
         story: "\n".join(outputs) if outputs else None
@@ -56,7 +56,7 @@ def clean_paragraph(entry):
 
 def reset():
     return {
-        user_outputs: None,
+        user_outputs: [],
         story: None
     }
 
@@ -70,7 +70,7 @@ with gr.Blocks() as demo:
     story = gr.Textbox(interactive=False, lines=20)
     story.style(show_copy_button=True)
 
-    user_outputs = gr.State()
+    user_outputs = gr.State([])
 
     prompt = gr.Textbox(placeholder="Continue the story here!", lines=3, max_lines=3)